1. Field of the Invention
The present invention relates to an optical device assemble apparatus for positionally aligning a set of optical devices including, for example, a matrix liquid crystal display device and a microlens array and for adhering the optical devices to each other with a photo-curing adhesive resin.
2. Description of the Prior Art
These days, a liquid crystal display device including two substrates and a liquid crystal enclosed therebetween is employed not only in a direct vision display apparatus, in which an image on the display device can be seen, but also in a projection display apparatus for projecting an image on a screen by transmitting a light through the display device. An example of the projection display apparatus is used for a projection TV.
When an enlargement ratio for projecting the image on the screen is improved in the projection display device, the number of pixels of the liquid crystal display device is required to be increased. Improving the enlargement ratio without increasing the number of the pixels results in an inferior quality image having lower precision.
However, an increase of the number of the pixels disproportionately enlarges a non-pixel area, which is not occupied by the pixels. Accordingly, the ratio of a black matrix covering the non-pixel area is heightened, and the ratio of an area of the pixels forming an image is lowered. This means that the ratio of openings of the liquid crystal display device is lowered. Such a phenomenon darkens a display plane of the liquid crystal display device, thus deteriorating the display quality. This problem is especially serious in an active matrix liquid crystal display device.
Japanese Laid-Open Patent Publication Nos. 60-165621 through 60-165624 disclose an apparatus for preventing such a deterioration of display quality caused by the reduction of the ratio of the openings. According to these patents, a liquid crystal display device has a microlens array on a surface thereof. Since the microlens array includes microlenses arranged in correspondence with the pixels of the liquid crystal display device, the light which would be blocked by the black matrix without the microlens array is converged in the pixels. As a result, the display plane is brightened, which improves the display quality.
Examples of this type of microlens include a semispherical microlens having a semispherical concave portion on a surface of a substrate thereof and a flat microlens having a refraction factor distributed inside a substrate thereof.
In such an apparatus, the microlens array is assembled with the liquid crystal display device. The applicant of the present invention has disclosed an example of such assembly in Japanese Laid-Open Patent Publication No. 1-187715. An ultraviolet ray-curing adhesive agent is painted all over a surface of one of the substrates, and microlenses are placed on the surface. Then, an ultraviolet ray is radiated to cure the adhesive agent, thus adhering the microlens array on the liquid crystal display device.
The ultraviolet ray-curing adhesive agent is desirable for the following reasons:
(1) A substrate having the liquid crystal display device thereon and a substrate having the microlens array are possibly formed of different materials. If a heat-curing resin is used as the adhesive agent, the two substrates are possibly positionally displaced or separated from each other by a difference in the coefficient of thermal expansion. PA1 (2) A resin which is cured at room temperature takes longer to cure and has a smaller adhering strength than the photo-curing or the heat-curing resin.
The microlens array and the liquid crystal display device are required to be positionally aligned with high precision before being assembled. The positional alignment is conventionally done, for example, by a method used for positionally aligning two substrates of the liquid crystal display device. This method will be described with an example in which the two substrates of the liquid crystal display device are positionally aligned. An electrode pattern is formed on an inside surface of each substrate. A cell gap between the substrates is set to be several micron meters. The substrates are moved with respect to each other by a microscopic distance so that markers formed in advance on the substrates are included in an area of a depth of focus of the microscope.
After the positional alignment is finished, the substrates are temporarily adhered to each other at several peripheral portions with an instantaneous adhesive agent or by partially curing the ultraviolet ray-curing resin with light radiation. Then, the substrates having a liquid crystal therebetween are heated to cure a heat-curing resin for sealing the liquid crystal. As a result, the substrates are completely adhered.
The aforementioned markers are formed by emitting a light from a halogen lamp, and the ultraviolet ray is emitted from a light source other than the halogen lamp.
In the case that such a conventional method is used to paste the microlens array and the liquid crystal display device, there occurs the following problem. A marker which is formed on a surface having the microlens array is to be aligned with one of the markers of the liquid crystal display device. The markers to be aligned have a gap therebetween, which corresponds to a thickness of the substrate having the above one of the markers. Since an ordinary microscope cannot focus on both of the markers simultaneously, precise positional alignment cannot be done quickly.